Not that I have, just surprised that Sky wouldn't take my money.
Not unless they have changed their T and C's to allow it, they never did before.
(d) Sky Broadband will be provided to you at the address of your home in the UK that you notify to us from time to time ("Address"). If you are a Sky TV customer you can only have one Sky Broadband subscription per Sky TV Contract (excluding any Sky Multiroom subscriptions).
More to the point though, if you had two lines, both supplied by Sky with one on ADSL and the other of vDSL, they both end up in the same kit at the telephone exchange.
The only area where they don't share an identical path would be between the first cabinet and the telephone exchange.
So unless someone accidentally put a jack through the underground telephone trunking, or a fault developed in one of the cables, you would end up with both failing at the same time in most cases.